This study will determine when to perform prophylactic surgery for the prevention of diverticulitis recurrence. Background and Significance: Diverticulitis is a common clinical condition, especially among the elderly. In 1997, Medicare spent 375 million dollars on part A payments alone. Since recurrent attacks are common, prophylactic surgery is advised after one or more attacks of diverticulitis to reduce morbidity and mortality but the timing of prophylactic surgery is controversial. Some experts recommend surgery after the second attack of diverticulitis, while others advise it after the third attack. No studies have examined the merits of one strategy versus another. This study will help to define the best time to perform prophylactic surgery and thereby improve the cost-effective care for these patients. Research Design and Methods: This study will use a computer model (Markov) to analyze the experience of a hypothetical cohort of 65-year olds over a 5-year period. The model will examine 3 strategies: l.) Prophylactic surgery after the first attack of diverticulitis, 2.) Prophylactic surgery after the second attack of diverticulitis, and 3.) Prophylactic surgery after the third attack of diverticulitis. The transition state probabilities will be obtained from published data after a careful literature review. The main outcomes for the model will be costs and years of life. The economic perspective will be from the federal government. This study will consider only direct medical costs. Hospital costs will be estimated using the Prospective Payment System. Physician costs will be assessed using the Medicare Fee Schedule. A discount rate of 3 percent will be used. A one-way sensitivity analysis will be performed for all variables. The average cost and number of life years per patient will be calculated for each strategy. Cost-effectiveness ratios will be determined for each strategy.